Embodiments of the present invention relate generally to stacked electronic circuit boards and more specifically to improved encapsulated stacked electronic circuit boards.
It is known generally that heat is the enemy of electronic functionality, and that it is advantageous to conduct heat away from electronic components as effectively as possible. Heat may be induced by ambient conditions or from the electrical circuit boards themselves. One way to remove heat is to mount high heat producing components, like semiconductors, to metal clad (or metal backed) circuit boards and then mount the unpopulated surface of the metal clad circuit boards to a suitable heat sink or heat conduction medium such as a die cast or extruded aluminum housing. Any heat generated is transferred though the metal which provides a greater surface area to disperse the heat more rapidly in addition to reducing localized hot spots. However, metal clad circuit boards are limited in regards to design options, such as the fact that you can not put circuit vias through the metal layer as you can with a circuit board made of dielectric material. Because of the limitations it is typical that high power circuits built on metal clad circuit boards are built using single layer (or single sided) boards.
There are also situations wherein the physical constraints imposed on the packaging of an electronic assembly and the nature of the circuits encompassed make it desirable to construct the total circuit using stacked boards interconnected by pins even when the constraints associated with metal clad circuit boards are not a factor.
Commonly, All Terrain Vehicles (ATVs) employ electronic systems involving high power handling devices along with somewhat complex control circuits. One example would be electronic voltage regulators. The regulators are used to rectify and regulate alternating current (AC) generated by an AC Generator (ACG), typically driven from the engine crankshaft. Due to metal clad boards typically being confined to a single circuit board side it becomes difficult to make connections to all required points on a circuit, as such, the circuitry placed on the metal clad baord must be relatively simple. A preferred method to accommodate more complex circuitry, is to stack multiple boards.
Printed circuit boards constructed using insulating (or substitute “dielectric”) materials as the base allow for the use of plated through holes and vias to pass signals between various layers on a multi-layer board and more simply from top to bottom on double sided boards. At the points where signal connections need to be made to the metal clad board, pins are soldered to the appropriate points, the pins being perpendicular to the plane of the metal clad board. Therefore, at least one circuit is laid out on a double-sided, or if necessary a multi-layer, control board with holes located appropriately to receive the pins from the metal clad board.
Furthermore, because voltage regulators are used on engine powered sports equipment, they are exposed to significant amounts of shock, vibration, moisture and other contamination. It is common practice to fully encapsulate the circuits. However, when the space between the two circuit boards is filled with the encapsulation compound and the assembly gets hot due to ambient or self generated heat, the expanding encapsulant can generate destructive forces attempting to push the circuit boards away from each other. These forces put tensile stress on the pins, and shear and tensile stress on the solder joints which can cause the pin solder joints to be broken.
Accordingly, the art of encapsulated circuit boards would benefit from an encapsulated circuit board which reduced the shearing of connecting pins due to expansion of the encapsulant.